Biology

I studied biology a couple years ago. I guess I mostly slept through it in high school, because I sure didn’t remember much. When we got to the section on DNA, I was like, “Holy shit, it’s a computer program!” DNA isn’t just roughly analogous to programming; it’s basically the same thing.
When a living cell needs to produce something, the nucleus cuts-and-pastes a string of instructions out of DNA, picking the right short chunk out of a string billions long.